package read

import (
	"mal-go/hash_map"
	"mal-go/symbol"
	"mal-go/vector"
	"strconv"
	"strings"
)

func ReadString(s string) (any, any) {
	res, err, _ := readForm(s, 0, "user")
	return res, err
}

func isDigitChar(c byte) bool {
	return c >= '0' && c <= '9'
}

func isSpaceChar(c byte) bool {
	return c == ' ' || c == '\n' || c == ','
}

func isSymbolChar(c byte) bool {
	return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || c == '_' || c == '-' || c == '/' || c == '\'' || c == '+' || c == '-' || c == '*'
}

func readForm(s string, pos int, ns string) (any, any, int) {
	if pos >= len(s) {
		return nil, "unterminated input", pos
	}
	c := s[pos]

	var res, err any

	if isSpaceChar(c) {
		res, err, pos = readForm(s, pos+1, ns)
	} else if isDigitChar(c) {
		res, err, pos = readInt(s, pos, ns)
	} else if isSymbolChar(c) {
		res, err, pos = readSymbol(s, pos, ns)
	} else {
		switch c {
		case '{':
			res, err, pos = readMap(s, pos, ns)
		case '[':
			res, err, pos = readVector(s, pos, ns)
		case '(':
			res, err, pos = readList(s, pos, ns)
		}
	}
	return res, err, pos
}

func readMap(s string, pos int, ns string) (any, any, int) {
	m := hash_map.New()
	return m, "unimplemented", pos
}

func readList(s string, pos int, ns string) (any, any, int) {
	pos += 1
	forms := vector.New()
	for rune(s[pos]) != ')' {
		res, _, pos2 := readForm(s, pos, ns)
		forms = forms.Conj(res)
		pos = pos2
	}
	return forms.ToList(), nil, pos + 1
}

func readVector(s string, pos int, ns string) (any, any, int) {
	pos += 1
	forms := vector.New()
	for rune(s[pos]) != ']' {
		res, _, pos2 := readForm(s, pos, ns)
		forms = forms.Conj(res)
		pos = pos2
	}
	return forms, nil, pos + 1
}

func readInt(s string, pos int, ns string) (any, any, int) {
	startingPos := pos
	c := s[pos]
	for isDigitChar(c) {
		pos += 1
		if pos >= len(s) {
			break
		}
		c = s[pos]
	}
	res, _ := strconv.Atoi(s[startingPos:pos])
	return res, nil, pos
}

func readSymbol(s string, pos int, ns string) (any, any, int) {
	startingPos := pos
	c := s[pos]
	for isSymbolChar(c) {
		pos += 1
		if pos >= len(s) {
			break
		}
		c = s[pos]
	}
	sym := s[startingPos:pos]
	symNs := ns
	if strings.Contains(sym, "/") {
		splitIdx := strings.Index(s, "/")
		symNs = s[startingPos:splitIdx]
		sym = s[splitIdx+1 : pos]
	}
	return symbol.Intern(symNs, sym), nil, pos
}